Our co-pending application WO02/016995, the disclosure of which is incorporated herein by reference, describes and claims such an arm. The arm has a work head adapted to carry a tool or examination element for work or examination at a site, and operating means for operational control of the work head. The arm is adapted to be able to reach the site in a ‘tip following’ manner to position the work head in a desired operating position. This is achieved with control means controlling the position and/or attitude of each arm segment relative to a datum thereby enabling the arm to follow and adapt to a predetermined path.
Robotic arms of this type may be referred to as “snake arms”, since they have the ability to advance longitudinally along their own length thus enabling them to follow a serpentine path. This has the advantage that arms of this type may be used in circumstances where access to a work site is severely restricted.
For example, in some such snake arms, the articulation of the links in each segment may be controlled with precision to enable the arm to follow a convoluted path to guide a work tool into, for example, a restricted access pathway within a machine or a lumen of the human body.
Such a construction, however, requires precision engineering of each component to minimise frictional losses at the point of articulation between each pair of links. In a multi-link segment arm, these friction losses build up and the overall friction losses to be overcome during manipulation of the arm can be considerable. There is a need, therefore, for a device in which the manufacture of the components is relatively straightforward and in which the friction losses are significantly reduced.
In the arm forming the subject of WO02/016995, each segment is controlled by driven control cables terminating at the distal end of the segment. Springs are provided to bias each of the links against the compressive force exerted by the control cables in order to reduce friction. While successful in achieving its object, this further adds to the complexity of the system and hence to the complexity and cost of manufacture.
An alternative approach is set out in our co-pending application WO02/100608, the disclosure of which is also incorporated herein by reference, which dispenses with the springs and interposes instead a layer of rubber or elastomeric material either bonded or keyed to the two members constituting the articulation between adjacent links within a segment, the rubber providing the resilient shear capacity necessary to produce “stiffness” of the joint. While this arrangement is eminently satisfactory, it does again add to the complexity of construction. The present applicants have found that by using at least one spring which is interconnected to the series of individual links within a segment, significant advantages accrue in terms of manufacturability, increased axial loading and torsional stiffness, and indeed increased options in the properties of the resultant arm.